Akuma no Ken de Tenshi wo Kurau

With the demon sword in hand, he slashes through monstrous beasts...!! Suddenly appearing in Japan, the ‘Heavenly Prison’. The ‘treasure’ slumbering within this vast labyrinth overrun by monstrous beasts brought prosperity back to Japan. By chance, Jinya Kokucho acquired the “demon sword” needed to survive this dungeon, and whether he liked it or not, he found himself drawn into trouble. Suddenly appearing, a monster called the ‘Angel’ in an isolated prison he cannot leave until he destroys the ‘Nuclear Stone’, and the ‘Void Sword’. Plus, a woman's voice echoing in his mind. Jinya's peaceful days come to an end, and a new life, like a life-or-death tightrope walk, begins... (Source: Kadokawa, translated)